True, however I have to assume that fuel tanks tend to be lower on the locomotives (and therefore nearer the tracks), so as long as the explosive is high enough energy to set off the fuel, it’ll do a lot of the work for you. As will momentum, because all the explosive has to do is damage the tracks and jostle the engine, and the length of cars behind will keep on moving, go of the rails, and slam into the fireball.
There are some commercial rolls I’ve seen in the US that seem to be a happy medium…the holder itself in the stall has a thin plastic rod for the TP to go on, and the rolls have a very small opening in the center (and no cardboard) to go on that rod.